Primordial rocks show early Earth as dynamic place

WASHINGTON (Reuters) - Scientists have identified an expanse of rock in Greenland as a remnant of Earth’s crust dating back 3.8 billion years, a finding that shows the dynamic geological process called plate tectonics was occurring early in our planet’s history.

The western shores of Greenland are shown in this September 2, 2004 file photo. Scientists have identified an expanse of rock in Greenland as a remnant of Earth's crust dating back 3.8 billion years, a finding that shows the dynamic geological process called plate tectonics was occurring early in our planet's history. REUTERS/Andy Clark

Writing in the journal Science on Thursday, a team led by Harald Furnes of the University of Bergen in Norway said these ancient layered rocks from southwestern Greenland originally were formed on the sea floor of primordial Earth.

They are made up of thin sheets of formerly molten rock, and look a bit like a multilayered cake. They contain a mix of volcanic rocks associated with the formation of new crust.

Plate tectonics is a theory broadly accepted by geologists relating to the movement of the gargantuan plates that make up the planet’s surface. These plates, largely corresponding to the continents, are in constant gradual motion.

Over millions of years, these plates move vast distances. Where they come together there can be significant geological activity like earthquakes, volcanoes and the creation of mountain ranges.

The fact that most of the continents look like puzzle pieces that fit together — with the western African coastline roughly matching with the east coast of South America — represents visual evidence of plate tectonics.

Earth is about 4.5 billion years old. Scientists have debated whether plate tectonics was taking place early in Earth’s history or merely in the second half of its history.

Because the Greenland rocks appear to have been formed in a characteristic mechanism of plate tectonics — the spreading of the ocean floor as plates move apart — they indicate that this important geological process was well under way 3.8 billion years ago.

“The southwest Greenland rocks are the oldest intact oceanic crustal rocks on Earth formed by sea floor spreading,” Furnes said by e-mail.

At the time, the Earth was almost unrecognizable from what it is today, and was far hotter. There is evidence that the first inhabitants of the planet had appeared in the form of bacterial life forms.

The Greenland rocks were originally mostly basalt, a hard volcanic rock, but over the eons have been transformed into a type of metamorphic rocks known as amphibolites, Furnes said.

These rocks are not the oldest-known ones on Earth, Furnes said, noting that rock dating to 4.2 billion years ago has been found in Canada.